Submersible pump drive system

ABSTRACT

A pump is coupled with a motor in a deep well to remove fluid of variable density. The downhole motor is energized from an electrical generator which produces substantially constant volts/hertz output energy. The generator has an input shaft to which a constant torque is applied from a variable drive unit. As the fluid becomes lighter, the downhole motor speeds up and the generator produces an increase in both frequency and voltage amplitude to maintain system efficiency.

United States Patent 1 Boyd 3,751,192 Aug. 7, 1973 SUBMERSIBLE PUMPDRIVE SYSTEM Clinton A. Boyd, Tulsa, Okla. Borg-Warner Corporation,Chicago, Ill.

Inventor:

Assignee:

Apr. 12, 1971 Filed:

Appl. No.:

US. Cl. 417/411, 318/432 IntrCl. F04b 35/04, 1102p 7/00 Field of Search417/411, 15,42,

[56] References Cited UNITED STATES PATENTS Primary Examiner-William L.Freeh Assistant Examiner-John T. Winburn I Attorney-Donald W. Banner,William S. McCurry and James J. JcnningsJr.

[57] ABSTRACT A pump is coupled with a motor in a deepwell to removefluid of variable density. The downhole motor is 3,226,6l9 l2/l965:Bloclc, 3l8/l48 X FOREIGN PATENTS OR APPLICATIONS 4/1927 Great Britain4l7/4ll A Torque Set 26 24 22 2| 20 Variable Speed Drive Constant DriveConstant 2 Torque Volts/Hertz energized from an electrical generatorwhich produces substantially constant volts/hertz output energy. Thegenerator has an input shaft to which a constant torque is applied froma variable drive unitJAs the fluid becomes lighter, the downhole motorspeeds up and the generator produces an increase in both frequency andvoltage amplitude to maintain system efficiency.

7 Claims, 2 Drawing Figures Switch A mid Board 4 PATENIED M18 7 25Torque Set 26 2); 22 2| 2? l8 Vorioble Fl id Drive s eed Gen. SW'TCh[)Eive Board Consront Consmunr.

Torque Volts/Hertz 4 Y @3 6 W c g xz FIG 1 5 i I v Z --*Fluid ,E Pump IAssembly Seol 5:; Moror 28 Motor 24 23 22 Inventor Clinton A BoydAttorney SUBMERSIBLE PUMP DRIVE SYSTEM BACKGROUND OF THE INVENTION Therehave long been problems in removing a fluid such as crude oil from adeep well. A motor and pump assembly is generally positioned at thedownhole location, and energized from electrical equipment at thesurface. With this arrangement the downhole motor drives the pump,raising the fluid through a conduit to the surface. For efficiency themotor-pump assemblyat the downhole location is sized or rated for thefluid density at a particular location. After the equipment has beenoperating, the denser fluid is pumped off and thereafter lighter fluidis raised through the conduit.

This lighter fluid presents a reduced load to the downhole equipment andthe efficiency of the system is reduced. Various attempts have been madeto maintain system efficiency. For example the downhole fluid densitycould be sensed, the motor speed sensed, or some other parameter sensedto provide an indication of the varying load. This signal may be fedback to the surface to regulate equipment, such as an electricalinverter, for varying the energization level provided to the downholemotor as a function of changing load. Of course there is additionalexpense in providing the feedback signal and the regulating arrangementat the surface. In addition, the added electrical conductors necessaryto return the feedback signal can be damaged, and disable the regulatingarrangement.

It is therefore a primary consideration of this invention to provide asubmersible pump drive arrangement in which the efficiency of thedownhole unit is maintained although the fluid density varies.

A related consideration of this invention is the provision of such asystem, without any feedback arrangement or the necessity for sensingthechanging load conditions at the downhole location.

SUMMARY OF THE INVENTION The present invention is useful for removing afluid of variable density from a deep well position through a conduit toa surface location. The system includes a pump which is positioned inthe well, and coupled to the conduit to remove the fluid as the pump isdriven. An electrical motor is also positioned in the well, and coupledto the pump to drive the pump when the motor is energized. At thesurface location is an electrical generator having an input shaft, andhaving output connections coupled over an electrical cable to thedownhole motor, to energize the motor as the generator is driven overits input shaft.

In accordance with the present invention, a variable drive unit iscoupled to the generator input shaft. This variable drive unit is of thetype which displaces the generator input shaft at a constant torquelevel. A motor, internal combustion engine, or other unit can be used tosupply energy to the variable drive unit which provides the constanttorque. As the fluid density decreases, the downhole motor speeds up,and the electrical generator also increases its speed. This speedincrease of the generator in turn increases the frequency and theamplitude of the voltage supplied to the motor, maintaining a highefficiency for the complete system.

THE DRAWING nected in accordance with the inventive teaching: and

FIG. 2 is a partial block diagram illustrating an alternate system forsupplying energy to the variable speed drive of the system.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 depicts an arrangement ofthe present invention for removing fluid 10 of variable density from adeep well 11. Assembly 12 positioned within the bottom of the wellincludes a pump 13 coupled through a seal 14 to an electrical motor 15.When energy is supplied over cable 16, motor 15 drives the pump 13 andlifts the fluid upwardly through a conduit 17 for discharge at thesurface.

At the surface location a switchboard 18 is shown for receiving inputelectrical energy over cable 20 and passing output energy over cable 16to the downhole motor. The electrical switchboard may include atransformer, protective relays, or other equipment conventionallyincorporated in such a system. For purposes of explaining andunderstanding the present invention, the switchboard and attendantcomponents are not necessary.

An electrical generator 21 has an input shaft 22, and electrical outputcontacts (not visible) coupled to the conductor 20 for transferringenergy over cable 16 to the downhole motor. In accordance with animportant aspect of this invention, a constant torque is applied to theinput shaft of generator 21. Another significant aspect of the inventionis that generator 21 is wound to provide a substantially constant ratioof the amplitude to the frequency of its output voltage. In the art thishas generally been termed Constant volts-per-cycle" operation. With theadvent of the hertz unit, it is now frequently termed Constantvoltz/hertz operation. For example the generator 21 might be wound andmechanically constructed to operate satisfactorily at 90 cycles persecond (or 90 hertz), even though its base speed would be at hertz. Thephysical arrangement would be such that as the generator speeds up, itsfrequency gradually increases to 90 hertz with a concomitant increase inthe voltage amplitude by 50 percent. In this way the magnetization ofthe downhole motor 15 is maintained substantially constant, applying aconstant torque to pump 13.

The constant torque is applied to the shaft 22 by variable speed drivearrangement 23. This can be a variable clutch, or variable speedcoupling, or any other arrangement which receives a mechanical inputdrive over its shaft 24 and provides a virtually constant torque to thegenerator shaft 22. To accommodate different systems, a torque set knob25 can be provided. This torque set 25, by way of example, can be thecontrol handle of an lNFl-DRIVE (Reg. Trademark) adjustable speed driveavailable from the Borg-Warner Industrial Drives division in Tulsa,Oklahoma. Of course any other suitable drive may be substituted, so longas the constant torque can be provided to the input shaft 22 ofgenerator 21. In general such a drive accommodates the driving speed toload variations so that the requisite constant torque is maintained.

Drive unit 26 shown generally in FIG. 1 can be an internal combustionengine, diesel engine or any suitable arrangement for providing therequisite displacement of shaft 24 to the variable speed drive unit 23.Of course drive unit 26 can be replaced by a second electrical motor 27,receiving a-c energy over an input cable or line 28 to supply power tothe system. The precise equipment utilized to provide the input angulardisplacement on shaft 24, and the constant torque on input shaft 22 ofthe generator, are not restrictions on the present invention. It is theprovision of this constant torque, together with a generator whichprovides a virtually constant output voltz/hertz ratio, that contributesto the enhanced efficiency achieved with this arrangement.

In operation, the system is initially set to operate for the heavierload condition of the downhole fluid. For example, generator 21 may beproducing output voltage at approximately 60 hertz and a given voltageamplitude under these conditions. As the fluid becomes lighter, pump 13encounters a reduced load and motor 15 tends to speed up. Withmaintenance of the constant torque on input shaft 22 of generator 21,the speed and thus the frequency of generator 21 gradually increases,with a simultaneous increase in the amplitude of its output voltage.This maintains a constant energizing current for the motor 15, andprovides a virtually constant torque to pump 13. This in effect matchesthe entire system to the variable density of the fluid at the downholelocation.

SUMMARY The present invention achieves a high efficiency without anyrequirement of a feedback signal to modulate the energy supplied overcable 16 to the downhole motor 15. By providing a virtually constanttorque to the generator, which generator in turn provides a constantvolts/hertz ratio in its output voltage, the system (in effect) changesthe size or rating of the downhole pump without the necessity of haulingthe entire assembly 12 to the surface and making a physical change inthe pump. For such a pump its capacity varies as a function of speed,and the head varies as the square of the speed. By maintaining aconstant torque to the downhole pump while allowing it to speed up whenthe fluid becomes less dense, the desired economy and effi-' ciency ismaintained without the necessity of a feedback system. In one suchinstallation, the incorporation of the arrangement depicted in FIG. 1increased the production of the well from 220 to 500 barrels per day.This is a striking manifestation of the increased efficiency availablewith the system depicted in FIG. 1.

While only particular embodiments of the invention has been describedand illustrated, it is manifest that various modifications andalterations may be made therein. It is therefore the intention in theappended claims to cover all such modifications and alterations as mayfall within the true spirit and scope of the invention.

What is claimed is:

1. An energizing system in which an electrical motor is coupled to apump for pumping fluid of varying density, comprising:

an electrical generator connected to supply energy over a cable to themotor, such that the voltage amplitude is always maintained with asubstantially constant ratio to the frequency of the energy supplied;and

means coupled to the input shaft of the generator, for

supplying input mechanical energy at a substantially constant torquelevel to the generator, allowing the generator to produce an increasedoutput voltage at an increased frequency as the pump speeds up when thefluid becomes less dense.

2. An energizing system as claimed in claim 1, in which the pump and theelectrical motor are disposed in a well, and a conduit provided toremove the fluid from the well as the pump is driven.

3. An energizing system as claimed in claim 1, in which the means forproviding a constant torque on the generator input shaft includes avariable speed drive arrangement connected to the input shaft, and adrive means is connected to supply energy to the variable speed drivearrangement.

4. An energizing system as claimed in claim 3, in which the variablespeed drive arrangement includes an adjustment setting for establishingthe level of torque to be supplied over the input shaft to thegenerator.

5. A system for moving a fluid of variable density from a deep wellposition through a conduit to a surface location, including:

a pump positioned in the well and coupled to the conduit to remove thefluid as the pump is driven;

a first electrical motor positioned in the well, and coupled to the pumpfor driving the pump when the motor is energized;

an electrical generator having an input shaft, positioned at the surfacelocation'and coupled to the first motor over an electrical cable toenergize the motor, such that the generator output voltage supplied tothe motor has a substantially constant amplitude/frequency ratio overthe generator operating range;

a variable drive unit, coupled to the generator input shaft fordisplacing the shaft at a constant torque; and

means for supplying energy to the variable drive unit.

6. A system as claimed in claim 5, in which the variable drive unitincludes means for adjusting the level of the torque transferred to thegenerator input shaft.

7. A system as claimed in claim 5, in which a second motor is connectedto supply energy to the variable drive means, and electrical energy issupplied to the second motor to drive the input shaft of the variabledrive means.

I? i i l I

1. An energizing system in which an electrical motor is coupled to apump for pumping fluid of varying density, comprising: an electricalgenerator connected to supply energy over a cable to the motor, suchthat the voltage amplitude is always maintained with a substantiallyconstant ratio to the frequency of the energy supplied; and meanscoupled to the input shaft of the generator, for supplying inputmechanical energy at a substantially constant torque level to thegenerator, allowing the generator to produce an increased output voltageat an increased frequency as the pump speeds up when the fluid becomesless dense.
 2. An energizing system as claimed in claim 1, in which thepump and the electrical motor are disposed in a well, and a conduitprovided to remove the fluid from the well as the pump is driven.
 3. Anenergizing system as claimed in claim 1, in which the means forproviding a constant torque on the generator input shaft includes avariable speed drive arrangement connected to the input shaft, and adrive means is connected to supply energy to the variable speed drivearrangement.
 4. An energizing system as claimed in claim 3, in which thevariable speed drive arrangement includes an adjustment setting forestablishing the level of torque to be supplied over the input shaft tothe generator.
 5. A system for moving a fluid of variable density from adeep well position through a conduit to a surface location, including: apump positioned in the well and coupled to the conduit to remove thefluid as the pump is driven; a first electrical motor positioned in thewell, and coupled to the pump fOr driving the pump when the motor isenergized; an electrical generator having an input shaft, positioned atthe surface location and coupled to the first motor over an electricalcable to energize the motor, such that the generator output voltagesupplied to the motor has a substantially constant amplitude/frequencyratio over the generator operating range; a variable drive unit, coupledto the generator input shaft for displacing the shaft at a constanttorque; and means for supplying energy to the variable drive unit.
 6. Asystem as claimed in claim 5, in which the variable drive unit includesmeans for adjusting the level of the torque transferred to the generatorinput shaft.
 7. A system as claimed in claim 5, in which a second motoris connected to supply energy to the variable drive means, andelectrical energy is supplied to the second motor to drive the inputshaft of the variable drive means.